检查int是否为主要Java [英] Check if an int is prime Java

问题描述

抱歉修复我的代码"帖子

与质数相比，与 for 循环的语法更多相关，现在也已解决.

related more to syntax of a for loop than prime numbers, also solved now.

我的任务是从控制台获取一个int并打印(在单独的行上)从1到n(含)的所有质数.我的方法从n开始，检查其素数，然后将n递减1并循环直到n = 2.为了检查数字是否为素数，我运行了一个循环，检查将数字除以x的余数等于零，其中x从2开始并在root(n)处停止.现在，所有这些都在理论上可行，并且阅读我的代码后，我看不出它出了什么问题.

My task is to take an int from the console and print out (on separate lines) all the prime numbers from 1 to n inclusive. My method starts at n, checks if its prime, then increments n down by one and loops until n=2. To check if a number is prime I run a loop, checking is the remainder of diving the number by x is equal to zero, with x starting at 2 and stopping at root(n). Now this all works in theory, and reading my code I don't see where it goes wrong.

public class Prime {
public static boolean isPrime(int n) {
    boolean result = true;
    for (int x = 2; x>=sqrt(n); x++) {
        if ((n % x) == 0) {
            result = false;
            break;
        } else {
            x++;
        }
    }
    return result;
}

public static void main(String[] args) {
    Scanner intIn = new Scanner(System.in);
    int i = intIn.nextInt();
    while (i>=2) {
        if (isPrime(i)) {
            System.out.println(i);
            i--;
        } else {
            i--;
        }
    }
  }
}

例如，输入is 10将返回10(以及9,8,7,6,5,3)，即使isPrime()检查10％2 == 0，然后设置 result 为false.我在这里想念什么?

For example an input of 10 will return 10 (along with 9,8,7,6,5,3), even though isPrime() checks if 10 % 2 == 0, then sets result to false. What am I missing here??

我再次为烦人的问题(略有重复)道歉.

Again I apologise for the annoying (slightly duplicate) question.

推荐答案

for 循环中的条件是继续的条件，而不是停止.您需要将> = 替换为< = :

The condition in the for loop is the condition to continue the loop, not the condition to stop it. You need to replace >= with <=:

for (int x = 2; x<=sqrt(n); x++) {
    // Here -----^

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